1. Field of the Invention
The present invention relates to a dual mode cellular phone and, in particular, to a method for automatically switching a dual mode cellular phone to a digital or analog mode when a user is mobile.
2. Description of the Related Art
A dual mode cellular phone is compatible with both a digital Code Division Multiple Access (CDMA) communication system and an analog Advanced Mobile Phone Service (AMPS) communication system. This dual mode cellular phone is tuned to the digital communication system in a common service area where the digital and analog base stations are both installed, and to the analog communication system in an analog service area where only the analog base station is installed.
When the dual mode cellular phone is set to a digital preference mode, it is tuned to the digital base station in the common service area. However, in the analog service area, upon power-up, the dual mode cellular phone first attempts to search for the digital base station. If the search fails, then the dual mode cellular phone searches for the analog base station. Subsequently, the dual mode cellular phone is tuned to the analog base station, allowing the user to talk over the phone.
When the user terminates the call upon completion of the telephone conversation, the dual mode cellular phone again searches for the digital base station for a specified time (e.g., approximately 60 seconds). Similarly, even when the user terminates an incoming call after completion of the conversation, the dual mode cellular phone searches for the digital base station for the specified time. Further, even when the dual mode cellular phone is set to an analog mode, it searches for the digital base station in an idle state at specified time intervals (e.g., 3 minutes).
Searching for the digital base station disadvantageously causes the dual mode cellular phone to consume twice the amount of operating current as that consumed in the idle state. Further, and perhaps even more disadvantageous, the dual mode cellular phone cannot receive an incoming call during the search for the digital base station. Accordingly, the dual mode cellular phone may have a reduced call reception ratio and a reduced battery run-time.